The present invention relates to the use of unsaturated organic compounds for the stabilization of compositions which contain chlorofluoroalkanes and amines and/or polyols containing amino groups, and which, for example, are used for the production of polyurethane foams, a process for the stabilization of such compositions, the compositions themselves and stabilizer-containing chlorofluoroalkanes.
In the production of polyurethane foams, isocyanates are reacted with multivalent alcohols to form high molecular weight polymers which contain the polyurethane linkage. If foamed polymers are desired, a blowing agent, often a chlorofluoroalkane, is added to the isocyanate or the multivalent alcohol (polyol) or both. The blowing agent is evaporated by the heat of reaction resulting during polymerization and thus a foamed product of low density is obtained.
If the compounds needed for the production of polyurethane foams are mixed together immediately before the reaction, a foam material with good properties can easily be produced. For practical reasons, often only the diisocyanate components are stored separately until foaming. All other components required for the production of foam material, such as catalysts, e.g., amine catalysts, emulsifying agents and the blowing agent or blowing agent mixture are pre-mixed with the polyol. These pre-mixtures have to be storable for long periods before use, without a reaction or decomposition occurring which would adversely affect the quality of the foam material produced.
However, this procedure only works well with non-amine polyols, i.e., polyols which only contain carbon, hydrogen and oxygen as elements, provided that the pre-formulated compositions are not subjected to extreme temperatures during storage. In the case of amines (including aminoalcohols) and the case of polyols based on amines, i.e., polyols which contain nitrogen in addition to the stated elements carbon, hydrogen and oxygen, and which represent, e.g., amine or alkanolaminestarted polyethers with free hydroxyl groups, however, a reaction takes place between the amine or the amine-based polyol on the one hand and the chlorofluoroalkanes used as blowing agents on the other hand. This leads to the formation of hydrochloric acid which results in a decrease in the pH value and an accompanying decrease in the storage stability of the liquid compositions. Furthermore, the solution becomes darker, its viscosity increases, and only poor quality foam materials can be produced, or the compositions even become unusable for producing foamed materials.
It is known from West German Pat. No. DE 1 207 626 that unsaturated compounds ----such as butadiene, isoprene, styrene, .alpha.-methylstyrene or 1-alkenes with 4 to 18 carbon atoms ----can be added as stabilizers to these compositions which contain amine-based polyols as well as chlorofluoroalkanes; whereas unsaturated oxygen-containing compounds such as vinyl acetate or methyl vinylketones are described as ineffective for the same purposes.
U.S. Pat. No. 3,352,789 discloses that in addition to .alpha.-methylstyrene, anethole (=1-(p-methoxyphenyl)propene-1), m-diisopropenylbenzene, 1,3,5-triisopropenylbenzene and 1-(p-methoxyphenyl)-2-nitropropene-1 can be used for stabilization.
Furthermore, U.S. Pat. No. 3,465,052 describes the use of p-isopropenyl-toluene (p-methyl-.alpha.-methylstyrene), and U.S. Pat. No. 4,463,189 describes the use of an isomeric mixture of 2,4-diphenyl-4-methyl-pentenes ("dimeric .alpha.methylstyrene") to inhibit the reaction of the amines, the aminoalcohols or the polyol containing amino groups with the chlorofluoroalkane.
It is thereby disadvantageous that the aforementioned compounds fulfill their stabilizing function only for relatively short storage periods and even then in some cases unsatisfactorily. If a certain storage period is exceeded, reactions increasingly start to occur between the amine or the amine-based polyol and the chlorofluoroalkane. Just as with non-stabilized compositions, these reactions lead to a lowering of the pH value through the formation of hydrochloric acid and to an increase in viscosity. The compositions change their color, and become cloudy and also less reactive due to precipitation of hydrochlorides. Such aged compositions exhibit prolonged starting times on foaming, prolonged setting times and prolonged times for becoming free of tackiness. In addition they lead to poor quality foamed materials, i.e., dark-colored foamed materials with non-uniform cells which are often too large, or they even can no longer be used for the production of foamed materials.
A further drawback is that metals which are present may catalyze and accelerate the ageing process, which additionally reduces the maximum storage time upon usual storage of the pre-produced polyol compositions in steel plate containers or metal drums. In this case the corrosion of the containers, which is enhanced by the ageing of the compositions, causes additional problems.